In the field of absorbent structures for disposable absorbent articles like for example baby diapers, adult incontinence briefs, pads or sanitary napkins it has become common to use absorbent hydrogel material especially in particulate form. A large variety of designs improving the functionality of the absorbent hydrogel particles are known and are for example disclosed in EP-A-212 618, WO-9101163 or EP-A-325 416. More recently it has become known that many of the particulate absorbent hydrogel particles have an appreciable performance profile in respect to particle size. This has led to even further advanced absorbent structures utilizing the previously known amounts of absorbent hydrogel particles but limiting the particle size of the absorbent hydrogel particles to a specific range. Absorbent articles comprising structures of this or similar designs have been disclosed for example in U.S. Pat. No. 5,061,259 pending U.S. patent applications Ser. Nos. 07/684,712, 07/684,374 now U.S. Pat. No. 5,233,443, U.S. Ser. No. 07/684,633, U.S. Ser. No. 07/685,255 all filed on Apr. 12, 1991 or EP-A-339 461.
Since the specific particle size range required in these absorbent articles excludes the smaller particles, referred to as "fines" and defined hereinafter, the problem how to utilize these smaller absorbent hydrogel particles arose. This problem is for example disclosed in EP-A-417 761. Disposal of fines can almost be ruled out as a solution since it can cause an environmental problem and is commercially not attractive. As an alternative, the recycling of fines already during the manufacturing process of absorbent hydrogel particles is suggested in EP-A-463388 and EP-A-417761. However, the large quantities produced and the different production processes used for making absorbent hydrogel particles do not always allow immediate resolution of the problem by modifications of the manufacturing process. Also during transport interparticle friction between absorbent hydrogel particles can lead to fines being generated regardless of the initial particle size. In summary, these considerations suggest to search for alternative ways to utilize fines.
Therefore, it is an objective of the invention to utilize absorbent hydrogel particle fines in absorbent structures without incurring the problems previously resolved by selecting an absorbent hydrogel particle size distribution which omitted fines. It is also an objective of the invention to provide a process which allows to continue to utilize absorbent hydrogel particles of a full particle size distribution range thus eliminating the need for modifications to the manufacture of absorbent hydrogel particles.
In a different aspect of the invention a further improvement of the design of absorbent articles is provided by incorporation of the absorbent structures according to the present invention. A design characteristic of absorbent articles is that the liquid impervious backsheet requires protection from being penetrated by dry absorbent hydrogel particles to maintain liquid imperviousness. Some designs afforded the extra cost of a high basis weight backsheet strong enough to withstand penetration or marking by absorbent hydrogel particles. Other more practical designs included a protective layer of fibrous, often also absorbent, material between backsheet and the absorbent structure which comprises the absorbent hydrogel particles. This had the added advantage of supplying some extra absorbent capacity while protecting the backsheet. Two well known executions of this absorbent article design are either to include a tissue layer or, more preferably, creating an absorbent structure which had the absorbent hydrogel particles only distributed above a thin protective layer, designated dusting layer, of the absorbent structure. However, even this most advanced design including a dusting layer had the disadvantage that part of the absorbent structure was only utilized to a suboptimal extent since the dusting layer by design could not contain absorbent hydrogel particles.
Therefore, a third objective of the invention is to supply absorbent articles having a dusting layer to prevent penetration or marking of the backsheet by absorbent hydrogel material particles in which the absorptive function of the dusting layer is optimized by incorporation of absorbent hydrogel fines.
An additional objective of the present invention is to combine the elimination of problems associated with the utilization of absorbent hydrogel particles in absorbent articles with the improvements in absorptive function by including absorbent hydrogel particles in the dusting layer of absorbent structures.